


certain dark things

by la_muerta



Category: Shadowhunters (TV)
Genre: Alternate Universe - Canon Divergence, Double Penetration, M/M, Mildly Dubious Consent, Non-Consensual Bondage, Porn with Feelings, Tentacle Sex, True Love's Kiss, Virgin Shadowhunter Energy, lol what even is this fic
Language: English
Status: Completed
Published: 2019-08-17
Updated: 2019-08-17
Packaged: 2020-09-06 05:00:17
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 2,833
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/20285803
Author URL: https://archiveofourown.org/users/la_muerta/pseuds/la_muerta
Summary: In an alternate version of the universe, Alec doesn't meet Magnus while fighting off Circle members - doesn't have the opportunity to, because over a century ago, someone set a demon on the High Warlock of Brooklyn so powerful that it completely destroyed him. The demon was never caught, and rumour has it that it now lurks in the sewers of New York City, a terrible monster that has the ability to grant the most desperate wishes of those foolish enough to seek it.So when Clary Fray crashes into their lives, everything goes to hell much faster. By the time she finally gets her hands on the stupid spellbook that will wake her mother up, Izzy is locked up in the City of Bones awaiting de-runement and exile (no thanks to Alec's fiancée - which certainly puts a crimp in the wedding plans), and Jace has defected to Valentine with the Mortal Cup in hand.Alec is pretty damned desperate now.





	certain dark things

**Author's Note:**

> Seriously, read the tags.

Alec sneaks out of the Institute even though it's on lockdown and ends up wandering around in the sewers alone, armed with nothing but his stele, a seraph blade, and a witchlight stone, hoping to find the demon of legend. He can feel Jace's pain and fear through even through their weakened parabatai bond, and he doesn't know how much of the hopelessness he feels is feeding back to Jace. In a matter of days he's lost everything - his family has been torn apart, the Institute has been taken over by Victor Aldertree, and with his engagement to Lydia strained but still standing, he knows he has lost all hope of finding happiness in his future. 

Alec used to explore the sewers with Jace and Izzy when they were children, but it was always Izzy who knew the maze of dark tunnels like the back of her hand. Alec only has a vague sense of where he is because GPS sure as hell doesn't work down here, and he stumbles into the demon's lair almost by accident - or perhaps he was pulled in, because he's a lone shadowhunter blundering around in enemy territory. 

His first impression is that he's trapped in a gigantic black spiderweb, except that the strands of the web are slick and slippery rather than sticky. They coil around his wrists and ankles at lightning speed, forcing him to drop his blade and witchlight stone with a vicious twist, and one more coils itself loosely around his neck - not enough to choke him, just threatening to. 

Alec blinks, blind without light, but he can hear something moving towards him. 

"Well, well. What's one of the angel-born doing here in my disgusting little hellhole?" a voice in the darkness asks. The voice of the demon is deep and grating, but there is something human about its self-loathing. "Has the dashing hero finally arrived to slay the monster and save the city?" 

"I'm not here to try to kill you, I need your help. I need to rescue my parabatai from his father and break my sister out of the City of Bones," Alec says, forcing himself to go against every instinct to struggle against his restraints. 

"Everybody always comes around wanting something. The question is, can you afford the price?"

"As long as you can guarantee the safety of my sister and my parabatai, name it and it's yours," Alec says immediately. 

"That's not how you negotiate a deal, darling," the voice says in amusement. A light flares up, held in the palm of the demon, and Alec can finally see its face. 

It is a creature straight out of Alec's worst nightmares, not because it is repulsive or disgusting, but because it is beautiful, in a way. The demon has a humanoid form, all firm muscles and strong limbs. Its skin is pitch black with an oily purplish sheen, but it would be the perfect body of a human male if its hands and feet didn't end in razor-sharp black talons and it didn't have a few dozen appendages sprouting from its back like a cruel mockery of wings. But its face is what finally helps Alec realise why it makes perfect sense for the demon to look the way that it does - because some demons draw its victims in by seducing them, so it would make sense for the demon to take on the form of a handsome man to face Alec. 

"You must give me your proper name for the deal to be made." 

"Alexander Gideon Lightwood."

"Well, Alexander, my price is you - or your virgin shadowhunter energy, to be precise," the demon says. It has the smile of a shark, and the teeth to match. 

Alec hesitates, but if he's honest with himself, he knows he has nothing of worth to anybody. "Deal," he says.

The demon laughs, and the bonds on Alec's wrists and ankles tighten painfully. Long slippery appendages reach for him and begin tearing his clothes off, even his combat boots, shredding everything with unnecessary violence until Alec is completely naked. Alec's wrists are yanked above his head, and the demon's tentacles - because that's basically what they are - coil around his thighs and drag them apart with deliberate slowness, exposing Alec's ass and cock to the demon. 

Alec turns his face away from the demon and squeezes his eyes shut, but he lets his body go limp and doesn't fight it. What's the point? The demon named its price, and he agreed, fair and square. Something slick presses against his lips and his eyes fly open in shock to find one of the demon's black tentacles in his face. It's thicker than a finger, with a blunt tip, and it feels smoother than normal skin. Alec can feel the demon's yellow cat eyes watching him intently, waiting for him to resist, but Alec tamps down his revulsion and opens his mouth for the tentacle to slither in. 

It's not what he expected. It doesn't taste or smell vile like he expected it to, although it's definitely hotter than normal human body heat. The tentacle is muscular and oddly heavy on his tongue, but Alec has the uncomfortable, arousing feeling that this might be what it would feel like to have a dick in his mouth. He can feel it swelling inside his mouth and at first he tries to use his tongue to stop it from hitting the back of his throat and making him gag, but it pushes its way in and fills his mouth to a point that his jaw aches and his lips are stretched around its girth. It starts to fuck his mouth, and Alec struggles to breathe. He could bite down on it, but that would probably piss the demon off, so instead he closes his eyes and bears with it. 

Two other tentacles find his nipples, teasing and flicking them, one slides over his balls, and the tip of another tentacle starts rubbing around the rim of his entrance, and Alec starts to retreat inside his head. He signed up for this, he said yes, he thinks, as the tip of the slick tentacle starts to work its way inside his body. 

Something occurs to him - Lydia probably won't want to marry him anymore now that he's letting a demon fuck him, and it brings him immense relief. Alec has a moment of vicious satisfaction imagining himself walking into the Institute like this - clothes torn to shreds, lips swollen and abused by the demon's tentacle, and probably with the demon's come running down his thighs. Nobody will ever doubt the lengths Alec is willing to go to keep his family safe, and the Lightwood name isn't worth dirt anymore these days - so he might as well let it crash and burn with him. 

The demon is taking its time teasing him open with the tentacle, and when it finally reaches deep enough to find Alec's prostate, it is merciless - rubbing the bundle of nerves inside Alec until he starts to moan helplessly around the tentacle fucking his mouth. Alec's cock is getting hard, and he feels every flick at his nipples all the way down to his cock. There is no denying that his body is enjoying the stimulus, no matter how conflicted Alec feels about it. 

Alec reasons that it would be in his best interests to please the demon, so he gives the tentacle in his mouth a tentative suck, and the demon lets out a grunt of surprise. Emboldened, Alec sucks a little harder, and the demon makes a pleased sound. 

"Aren't you full of surprises," it purrs. 

Alec isn't expecting a swipe of something hot and wet right across the head of his cock. He looks down to see the demon grinning as it licks his cock again, and Alec can't help jerking away from the demon's mouth, because he really doesn't want those razor-sharp teeth anywhere near his cock, but the tentacles grip him tighter and the demon laughs as it fits its mouth around the head of Alec's cock and _sucks_. It shouldn't feel so good but it _does_, and Alec cries out as the slick heat of demon's mouth engulfs the full length of his cock. He can feel his balls drawing up tight, and it only takes a matter of seconds for the demon to make Alec come down his throat. Alec moans and shivers as the demon drinks every last drop of his release, and a strange ripple of light goes through the demon - through its body, and through the tentacles that have overtaken the entire space. 

_Virgin shadowhunter energy. _Alec didn't believe that was really a thing until now.

The tentacles in his mouth and ass withdraw, and Alec sags against the ones that are still coiled around his wrists, throat, and legs as the demon lets go of his spent cock. His jaw aches, the musky taste of demon slick still on his tongue, and he can feel the same slickness between his legs. He'd like to believe that the demon is done with him, but he knows he's got no such luck. 

As if reading his mind, the demon smirks and licks its lips, then leans forward and twirls its tongue around a nipple, and Alec bites down on the sounds that threaten to escape from him. There must be something in the demon's spit - it tingles a little even when the demon moves away, the heat of the demon's mouth lingering.

The demon teases his other nipple with his tongue and grins at him when Alec tries to stifle the whine at the back of his throat. "Oh no, that won't do. I want to hear all the pretty noises you make for me," the demon says. 

The demon spreads his legs further apart and turns him practically upside-down, making all his blood rush to his head, and Alec whimpers when the demon holds him open with its taloned hands and he feels the demon's tongue pushing into him. He's sensitive after coming so recently, and the demon's tongue must be longer than a normal human's because it slides right into him, unnaturally hot and making him sloppy with its strange tingling saliva. The demon seems to enjoy eating him out but it's too much, and Alec's whimpers become full-blown moans. Then the demon takes his half-hard cock inside his mouth and coats it with its spit before moving back to admire the sight of Alec squirming and panting in his grasp. 

The demon's saliva has a warming effect, almost to the point of pain but not quite, and Alec feels like he doesn't have enough blood in his body to spare between the blood rushing to his nipples, his ass, his cock, his head. Everything is hypersensitive but he _needs_ to be touched, and Alec is losing his grip on his self-control. 

"I can't take it anymore. Please," he grunts. 

"Please what?" 

"Take me."

The demon's voice drops lower. "Take you how?" 

"Fuck me, please, just fuck me," Alec gasps out. 

"Since you asked so nicely..." 

The demon rights Alec and pulls him towards him. His hands find Alec's hips, and then Alec feels the head of the demon's cock pushing at his entrance. It feels huge, bigger than the tentacle that was stretching him a while ago, and Alec can't stop himself from looking down to watch it thrusting into his body. It's too big and it hurts, and Alec already feels like his ass is on fire, but the demon is surprisingly patient, working his cock into him slowly until he is buried to the hilt, and another ripple of light goes through the demon.

Alec looks up and is surprised by the look on the demon's face - it has its eyes closed and head tilted back slightly, and it looks almost like it's at peace. Alec flexes involuntarily around the demon's cock inside him, and the demon opens his eyes and smiles. 

"Ah. You feel good, little Nephilim." It grinds its hips into him and Alec echoes its sound of pleasure. "So tight, and all mine."

The demon slides its cock halfway out of Alec's body, then slams back in, and Alec can't hold in the cry that it punches out of him. 

"Since you have been honest enough to give me your true name, I shall give you mine in return - my name is Magnus, and I want you to remember it for as long as you live," the demon murmurs in his ear, his cock still pressed deep into Alec's body. 

Something about that name is familiar, but Alec is distracted from puzzling it out when the demon thrusts into him again, and again, and Alec feels like he's breaking apart into a million brilliant shards. 

Alec has never felt pleasure like this. His leaking cock bobs against his stomach as the demon fucks his tight hole, and even the fact that his wrists are bound and legs are being forced apart only adds to the pleasure - there's nothing he can do to stop it, so he finally lets himself go and surrenders to the sensation. In a way this is a twisted version of something he's wished for in the shameful, secret recesses of his heart - to finally know how it feels like to have sex with a man. He moans wordlessly as the demon drives its cock into his ass, every thrust setting his nerves alight and sending waves of pleasure crashing through him. 

There are tentacles flicking his nipples again, but the demon doesn't put another one inside his mouth, preferring to bask in Alec's wanton cries of pleasure. The demon catches Alec's chin with two fingers, forcing Alec to look right into his eyes as he fucks him, giving Alec no chance to hide the lust-drunk look on his face. The expression on the demon's face is hungry, not for Alec's pain but his pleasure, and there's just something in its cat-like eyes - Alec should be repulsed by the obvious _other_-ness of them, but they are so expressive and _human_. 

"Kiss me," he says impulsively. 

"What?" The demon looks shocked. 

"Kiss me, Magnus."

The demon seems almost hesitant as it leans forward, and it's Alec who closes the last breath of distance to press their lips together. The demon's teeth should tear his lips and tongue to shreds but they don't, and if Alec keeps his eyes closed and doesn't think about who he's kissing, he can just lose himself in how good it feels. His second orgasm is building like a coil winding tighter and tighter in his gut, and a few more thrusts is all it takes for Alec to start coming, his cock completely untouched and the demon's name tumbling from his lips. A jolt of light goes through both of them and the demon lets out a guttural cry as it pushes deep into Alec's clenching body, and then it's coming too, cock throbbing inside Alec as it fills him with its release. 

The bonds around Alec's wrists, throat, and legs melt away into nothing, and Alec should be falling but there are warm arms around him. Alec reacts in kind and wraps his arms and legs around the demon's body instead of pushing it away - but something feels different now. 

The demon lowers him to the ground gently and snaps his fingers to conjure a light, and Alec startles. The demon looks completely human now, except for the cat eyes, and even though he can see the resemblance in the features, Alec would question if it was even the same being if this man's cock wasn't still buried deep inside Alec. 

"How...?"

"You freed me from my father's curse. I don't know how, but you did," the demon... man?... says, and he starts laughing but then he's crying too, collapsing into Alec's arms and heaving great ugly sobs. Alec is extremely confused but a lifetime of protective instincts kick in, even though all he can really do is hold Magnus close, letting his tears flow down his shoulder. 

By the time Magnus has calmed down and pulled himself together, his cock has slipped out of Alec's body, but their bodies are still a mess of come and demon slick. He cleans them both up and summons clothes for them with a wave of his hand, before immediately putting some distance between himself and Alec, and it hurts until Magnus starts apologising. 

"I'm so sorry, and I know words are cheap but I will do everything in my power to make it up to you, including rescuing your sister and parabatai - that is, if you still want my help," Magnus offers.

Sometimes things just begin in a different way, but the heart of the story remains the same. There is only one possible answer Alec can give in every variation of the universe, and he gives it without hesitation.

"Yes." 


End file.
